Components of the Circulatory System 1. Heart 2. Arteries 3. Arterioles 4. Blood Capillaries 5. Venules 6. Veins
Heart A muscular pump When it relaxes, it fills up with blood, and when it contracts, the blood is squeezed out with great force. The blood then circulates through the blood vessels.
Arteries Carry blood away from the heart Have thick, muscular, and elastic walls -> to stretch and recoil Contraction and relaxation of muscles in the arterial wall bring about constriction and dilation. Most arteries carry oxygenated blood.
Arterioles Arteries branch again to form tiny vessels called arterioles. Arterioles divide and ultimately their branches become capillaries. Regulates blood pressure.
Blood capillaries Are found between the cells of almost all the tissues. Have walls made up of endothelium. Endothelium is partially permeable. Capillaries branch repeatedly to provide a large surface area for exchange of gases.
Venules Capillaries unite to form small veins before it leave an organ or tissue. Allows blood to return from the capillary to veins.
Veins Carry blood back to the heart. The blood pressure in the veins is much lower than in the arteries. The walls in the veins are not as thick and muscular as arteries because blood flows more slowly and smoothly in the veins.
Veins Most veins have internal valves to prevent backflow of blood. The movement of blood along the veins is assisted by the action of skeletal muscles on the veins. Veins carry deoxygenated blood.
Tissue fluid A colourless liquid contained in the tiny spaces between tissue cells. The tissue cells are bathed with tissue fluid which carries substances in solution between the tissue cells and the blood capillaries.
How are substances transferred between capillaries and tissue cells?
Changing shape of red blood cells Red blood cells can only move through the lumen of the blood capillaries in a line. The red blood cells may become bell-shaped as they pass through narrow blood capillaries.
The Advantages of changing shape of red blood cell The diameter of the red blood cell is reduced. The cell increases its surface area. Rate of blood flow is reduced.